Magnetic tape and manufacturing method thereof, and servo writer

ABSTRACT

Abstract of the Disclosure 
     A magnetic tape is characterized in that a servo signal for performing tracking control of a magnetic head is written on a data band, data is recorded on the data band, and the servo signal is magnetized and written on the servo band magnetized in any one of direction of longitudinal directions with being magnetized in a reverse direction for the one direction.

Detailed Description of the Invention BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a magnetic tape where a servo signal toperform tracking control for a magnetic head is written, a manufacturingmethod thereof, and a servo writer.

2. DESCRIPTION OF THE RELATED ART

These years, in a magnetic tape a high density recording has progressedand there is the tape having a capacity of around 100 gigabytes for abackup of a computer. Therefore, several hundreds of data tracks areformed in the magnetic tape in a lateral direction. Accordingly, a widthof a data track extremely becomes narrow, and also a distance betweenadjacent data tracks extremely becomes narrow. Therefore, in order tomake a recording/reproducing element of a magnetic head trace the datatrack, a servo signal is written in the magnetic tape in advance andwith reading the servo signal by the magnetic head, a position of themagnetic head (position of the lateral direction of the magnetic tape)is servo-controlled (see Japanese Patent Laid-Open Publication No. Hei8-30942).

And the servo signal is recorded by giving a recording current to aservo band on non magnetized magnetic tape so as to magnetize the servoband in one direction.

In other words, as shown in FIG. 8B, conventional servo signals SS areformed on non magnetized servo bands SB by flowing a recording currentpulse PC consisting of a zero current and a plus pulse current as arecording current in order to avoid a saturation phenomenon of an MR(Magneto Resistive) element. If such the recording current pulse PC isused, as shown in FIG. 8B a magnetic tape MT is not recorded in areasexcept for servo patterns SP when the recording current pulse PC is thezero current; and when the plus pulse current of the recording currentpulse PC flows, the servo patterns SP are magnetized in one direction bya leak magnetic flux from a servo gap, thereby as a result the servosignals SS being written. On the other hand, in a magnetic taperecoding/reproducing apparatus a change point of a magnetization in theservo signals SS is detected with a change of an electric resistance bya servo signal reading element (MR element), and the change point of themagnetization as a read signal is output in a differential waveform(voltage value). Therefore, the larger the electric resistance of the MRelement becomes, the higher a peak value of the read signal of the servosignals SS, thereby an SN (Signal/Noise) ratio of the read signal beingimproved. Accordingly, when changes of the servo signals SS themselvesare large and when a read area is large due to a wide width of the servosignal reading element (MR element), as shown in FIG. 8C a peak voltagevalue of a read signal RSL of the servo signals SS becomes high.

Whereas, hereafter the high density recording of the magnetic tape isforeseen to progress till around several tens of terabytes. Therefore, anumber of data tracks of the magnetic tape, the width of the data track,and the distance between the adjacent data tracks become narrower, andthe magnetic tape itself becomes a thin layer. Based upon this, anamount of magnetism that is detectable in reading a servo signaldecreases and a change of a magnetization amount that is detectable withthe servo signal reading element also becomes small. Accordingly, asshown in FIG. 8D a peak voltage value of a read signal RSS of the servosignals SS becomes small, thereby the SN ratio of the read signal RSSworsening. As a result, in the magnetic tape recording/reproducingapparatus the servo signals SS becomes not able to be accurately read,thereby highly accurate position control of the magnetic head being notable to be performed.

Consequently, an improvement of the SN ratio of a read signal of a servosignal and a manufacturing method thereof are requested in the magnetictape.

SUMMARY OF THE INVENTION

In order to solve problems described above, a first aspect of thepresent invention is a magnetic tape where a servo signal for performingtracking control of a magnetic head is written on a servo band and datais recorded on a data band, wherein the servo signal is written on theservo band magnetized in any one direction of longitudinal directionswith being magnetized in a reverse direction of the one direction.

In such the magnetic tape the servo signal is configured of a patternthat is formed with being magnetized in the reverse direction on theservo band magnetized in any one direction of the longitudinaldirections, for example, toward a travel direction of the magnetic tape(this direction is assumed to be “forward direction”). Therefore, whenreading the servo signal with a servo signal reading element, a changerate and change amount of a magnetic field at a change portion of aservo pattern magnetized in the reverse direction for a base portion ofthe forward direction becomes large, thereby an output of the servosignal becoming high. Accordingly, the SN ratio of the read signal ofthe servo signal can be improved.

A second aspect of the present invention is, in the magnetic tape of thefirst aspect, characterized that the data band is not magnetized.

Although when data is recorded on the data band, it can be recorded bybeing overwritten without a demagnetization, magnetism originallyrecorded gives an influence in overwriting. However, in accordance withthe magnetic tape of the second aspect, the data band where data isrecorded is not magnetized, and therefore, when a signal is recorded, itcan be recorded in a preferable condition without having the influenceof the original magnetism.

In addition, in the magnetic tape described in the first and secondaspects, an effect of the present invention can be brought out when athickness of a magnetic layer is 10 nm to 300 nm.

A third aspect of the present invention is a manufacturing method of themagnetic tape described in the first aspect, wherein the manufacturingmethod has a first process for magnetizing a servo band to write atleast a servo signal in any one direction of longitudinal directions;and a second process for writing the servo signal on the servo band in astate where the servo band is magnetized in one direction by the firstprocess, with giving a servo signal recording head a recording currentpulse of a single polarity for magnetizing the servo band in the reversedirection of the one direction.

In accordance with such the manufacturing method, the servo band isone-directionally magnetized, for example, toward the travel directionof the magnetic tape (this direction is assumed to be “forwarddirection”) by the first process; and the servo signal is formed withmagnetizing the servo band by the second process. Therefore, since whenthe servo signal is read with a servo signal reading element of amagnetic head, a change rate and change amount of a magnetic field at achange portion of a servo pattern magnetized in the reverse directionfor a base portion of the forward direction become large, thus an outputof the servo signal becomes high. Accordingly, the SN ratio of a readsignal of the servo signal can be improved.

Moreover, a fourth aspect of the present invention is anothermanufacturing method of the magnetic tape described in the secondaspect, wherein the manufacturing method has the first process formagnetizing the servo band to write the servo signal in any onedirection of longitudinal directions; the second process for writing theservo signal on the servo band in the state where the servo band ismagnetized in the one direction, with giving the servo signal recordinghead the recording current pulse of the single polarity for magnetizingthe servo band in the reverse direction of the one direction; and andemagnetization process for demagnetizing the data band at a followingprocess of the first process and at any of a preceding and followingprocesses of the second process.

Thus demagnetizing the data band by the demagnetization process, themagnetic tape that can surely record data can be manufactured withouthaving an influence of original magnetism in recording the data.Meanwhile, a demagnetization is to defeat magnetism by giving a magneticfield of an alternating current, and for example, it means analternating current (AC) demagnetization.

A fifth aspect of the present invention is a servo writer used for themanufacturing of the magnetic tape described in the first aspect, whichwriter is equipped with a magnetic tape travel system that winds themagnetic tape sent out of a supply reel with a winder, thereby runningthe tape; a DC demagnetizing head for magnetizing at least the servoband in one direction of longitudinal directions of the magnetic tapewith contacting a magnetic tape that is running; and a servo write headfor writing the servo signal which head is provided at a downstream sideof the magnetic tape travel direction of the DC demagnetizing head,contacts the magnetic tape that is running, and thus magnetizes theservo band in the reverse direction.

In accordance with such the servo writer, after the servo band ismagnetized in one direction of the longitudinal directions of themagnetic tape with the DC demagnetizing head, a magnetization of theservo band is performed in the reverse direction with the servo writehead, so a magnetic tape that is high in a signal output in reading theservo signal, such as the magnetic tape described in the first aspect,can be manufactured.

In such the servo writer the DC demagnetizing head and the servo writehead are desirable to be integrally configured.

Thus configured, a relative position relationship of the DCdemagnetizing head and the servo write head can be fixed, and withouthaving an influence of a lateral directional vibration of the magnetictape, a portion of the servo band can be accurately magnetized in onedirection of the longitudinal directions of the magnetic tape.

In addition, a sixth aspect of the present invention is another servowriter used for the manufacturing of the magnetic tape described in thesecond aspect, which writer is equipped a magnetic tape travel systemthat sends the magnetic tape, whose all surface is magnetized in onedirection of longitudinal directions, out of a supply reel, and windsthe magnetic tape with a winder, thereby running the tape; an ACdemagnetizing head for magnetizing the data band with contacting amagnetic tape that is running; and a servo write head for writing theservo signal with contacting the magnetic tape that is running, and thusmagnetizing the servo band in the reverse direction.

In accordance with such the servo writer, the magnetic tape described inthe second aspect, where only the data band is demagnetized, that is,the data band is not magnetized, out of the magnetic tape whose allsurface is magnetized in the one direction of the longitudinaldirections, can be manufactured. Meanwhile, a position of the ACdemagnetizing head may be at any of an upstream and downstream sides ofthe servo write head for the travel direction of the magnetic tape.

In such the servo writer the AC demagnetizing head and the servo writehead are also desirable to be integrally configured.

Thus configured, it becomes difficult to receive an influence of alateral directional vibration, so only the data band can be accuratelydemagnetized. Meanwhile, “to be integrally configured” described aboveincludes to be configured by joining two components to one.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIGS. 1A, 1B, and 1C, FIG. 1A is an enlarged plan view illustrating amagnetization state of a magnetic tape related to an embodiment of thepresent invention; FIG. 1B is a drawing showing a servo read signal fromthe magnetic tape of FIG. 1A; and FIG. 1C is a recording current patternin writing the servo signal.

FIG. 2 is a plan view showing a magnetic tape related to a variationexample of FIGS. 1.

FIG. 3 is a drawing illustrating a part of a manufacturing process of amagnetic tape.

FIG. 4 is a configuration drawing of a servo writer used for writing aservo signal on a magnetic tape.

FIG. 5 is a plan view of a servo write head.

In FIGS. 6A and 6B, FIG. 6A is a configuration drawing of a servo writerof a third embodiment; and FIG. 6B is a variation example of FIG. 6B.

FIG. 7 is a configuration drawing of a servo writer of a fourthembodiment.

FIGS. 8A to 8D are drawings illustrating a magnetic tape with aconventional servo signal; FIG. 8A is a drawing showing a recordingcurrent in writing the servo signal; FIG. 8B is a plan view of themagnetic tape; FIG. 8C is a read signal of the servo signal when a widthof a servo read element is wide; FIG. 8D is a read signal of the servosignal when the width of the servo read element is narrow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention will be describedin detail, referring to the drawings as needed.

As a first embodiment, one example of a magnetic tape of the presentinvention will be described.

As shown in FIGS. 1A to 1C, a magnetic tape MT1 related to the firstembodiment has a plurality of servo bands SB1 extending in longitudinaldirections of the tape and data bands DB1 positioned between respectiveservo bands SB1. It is magnetized in the travel direction (see an arrowmark in FIG. 1A, and in the embodiment the direction is referred to as“forward direction” as needed) out of the longitudinal directions of themagnetic tape MT1. In FIG. 1A small arrow marks show a magnetizationdirection. And magnetizing the servo bands SB1 in the reverse direction,servo signals SS1 are written. The servo signals SS1 form each of servopatterns SP1 by: a burst Ba that is a magnetization portion like twostripes making a positively slanted angle for the travel direction(carrying direction) of the magnetic tape MT1; and a burst Bb that isfollowing the burst Ba and is the magnetization portion like two stripesmaking a negatively slanted angle for the travel direction. And theservo patterns SP1 are repeatedly formed at a predetermined distance inthe longitudinal directions, thereby the servo signals SS1 beingconfigured.

And the data bands DB1 between respective servo bands SB1 are alsouniformly magnetized in the forward direction. Of course, the magnetictape MT1 shown in FIG. 1A is a tape where no data is recorded, and whenthe data is recorded, magnetization portions in the forward directionand the reverse direction are formed on the data bands DB1, depending ona content of data.

Meanwhile, although in the embodiment each of the servo patterns SP1 isconfigured of each two of positively slanted stripes and negativelyslanted stripes, it is variable as needed, for example, such as beingconfigured of each five of the positively slanted stripes and thenegatively slanted stripes; and being alternately configured of eachfive of the positively slanted stripes and the negatively slantedstripes and each four of the positively slanted stripes and thenegatively slanted stripes. In addition, in FIG. 1A the servo patternsSP1 are drawn comparatively large for the magnetic tape MT1 in order tobe easily understood.

In FIG. 1A is shown a positional relationship of a magnetic head H forthe magnetic tape MT1. In the magnetic head H servo read elements SH forreading the servo signals SS1 are parallely provided in a lateraldirection of the magnetic tape MT1 (hereinafter simply referred to as“lateral direction) at a same distance as in the plurality of the servobands SB1. And between each of the servo read elements SH are provided aplurality of data write elements WH ranging in two lines in the lateraldirection of the magnetic tape MT1 in order to record signals on thedata bands DB1. Furthermore, between the data write elements WH areprovided a plurality of data read elements RH ranging in one line in thelateral direction of the magnetic tape MT1.

When for the magnetic tape MT1 thus described, data isrecorded/reproduced with the magnetic head H of a magnetic tape drive(not shown), the servo signals SS1 are read with the servo read elementsSH. Since the servo patterns SP1 of the servo signals SS1 are slantedfor the travel direction (equal to a longitudinal direction) of themagnetic tape MT1 and are formed by respective unparallel stripes, atiming when the servo read elements SH read the servo signals SS1 anddetect a pulse differs in accordance with relative positions in thelateral direction of the magnetic tape MT1 and the magnetic head H.Therefore, the data write elements WH or the data read elements RH canbe accurately positioned onto predetermined tracks of the data bands DB1by controlling a position of the magnetic head H so that a timing forreading the pulse becomes a predetermined condition.

Then, an output (peak voltage value) with which the servo read elementsSH read the servo signals SS1 depends on a change rate or change amountof a change between a portion where no signal is recorded and anotherportion where signals are recorded. And in the embodiment a magneticdirection largely varies from the forward direction to the reversedirection at a change portion from the base portion of the servo bandsSB1 magnetized in the forward direction to the servo patterns SP1magnetized in the reverse direction. In addition, the magnetic directionlargely varies from the reverse direction to the forward direction alsoat a change portion from the portion of the servo patterns SP1magnetized in the reverse direction to the base portion of the servobands SB1magnetized in the forward direction. Therefore, depending onthe large magnetic change, as shown in FIG. 1B, the servo signals SS1can be read with a high output. Accordingly, the SN ratio of readsignals of the servo signals SS1 can be improved.

In FIG. 2 is shown a magnetic tape MT2 that is a variation example ofthe magnetic tape MT1.

Although the magnetic tape MT2 of FIG. 2 also has a plurality of servobands SB2 extending in longitudinal directions and data bands DB2 sameas in the magnetic tape MT1, the servo bands SB2 are magnetized in theforward direction different from the magnetic tape MT1; and whereas thedata bands DB2 are not magnetized. When even such the magnetic tape MT2same as the magnetic tape MT1 reads servo signals SS2 with the servoread elements SH of the magnetic head H, read signals of a high outputcan be obtained, and thus the SN ratio of the read signals of the servosignals SS2 can be improved since signals are configured bycounterchanging the forward direction and the reverse direction. Inaddition, in accordance with such the magnetic tape MT2, since the databands DB2 are not magnetized, a magnetization can be sufficientlyperformed in a needed direction, thereby a recording of data being ableto be ensured.

Since the magnetic tape MT1 and the magnetic tape MT2 thus configuredare magnetic tapes whose magnetic layers are thin and whose width ofdata tracks is narrow, they are particularly effectively used when usedfor a magnetic tape drive where a width of the servo read elements SHfor reading the servo signals SS1 and the servo signals SS2 is narrow.That is, conventionally since a care must be taken for the saturationphenomenon of the MR elements, it is avoided to write a servo signal ina direct- current-magnetization portion with magnetizing the servosignal in the reverse direction; however when a magnetic layer is madethin and a width of a data track is made small in order to enlarge amemory capacity per volume, the configurations of the present invention,where a read output of the servo signal can be made high, becomessuitable.

As such a magnetic tape is preferable a case that an Mrt (product of amagnetic layer residual magnetization Mr and a thickness t of a magneticlayer) is 5.0x10⁻¹⁰ T•m (4.0x10⁻² memu/cm²) to 7.5x10⁻⁸ T•m (6.0memu/cm²); is more preferable another case that 5.0x10⁻¹⁰ T•m (4.0x10⁻²memu/cm²) to 5.0x10⁻⁸ T•m (4.0 memu/cm²); and is most preferable stillanother case that 5.0x10⁻¹⁰ T•m (4.0x10⁻² memu/cm²) to 2.5x10⁻⁸ T•m (2.0memu/cm²).

In addition, a Tw (track width of servo read elements) is preferable ina case of 0.1μm to 30μm, more preferable in another case of 0.1μm to15μm, and most preferable in still another case of 0.1μm to 7μm.

Furthermore, the thickness of the magnetic layer is preferable in a caseof 10 nm to 300 nm, more preferable in another case of 10 nm to 200 nm,and most preferable in still another case of 10 nm to 100 nm.

Describing suitable examples of magnetic tapes of the present inventionin more detail, the magnetic tapes, which have a non-magnetic layer anda magnetic layer on one face of a support body and a back layer on theopposite face thereof, are preferable. In addition, in a magneticrecording medium of the present invention the magnetic recording medium,which has layers other than the non-magnetic layer, the magnetic layer,and the back layer, are also included. For example, the recording mediummay has a soft magnetic layer containing soft magnetic powders, a secondmagnetic layer, a cushion layer, an overcoat layer, an adhesion layer,and a protection layer. These layers can be provided at adequatepositions so as to effectively bring out their functions. A thickness ofthe non magnetic layer can be made 0.5μm to 3μm: the thickness of thenon magnetic layer is desirable to be thicker than that of the magneticlayer.

Although a ferromagnetic powder for use in the magnetic layer of themagnetic recording medium of the present invention is not specificallyrestricted, a ferromagnetic metal powder and a hexagonal ferrite powderare preferable.

An average particle size of the ferromagnetic powder is preferably 20 nmto 60 nm. When the ferromagnetic powder for use in the present inventionis acicular and the like, the average particle size represented by anaverage long axis length is preferably 30 nm to 45 nm, and an averageacicular ratio is preferably 3 to 7; when the ferromagnetic powder isplaty, the average particle size is represented by an average platediameter, it is preferably 25 nm to 35 nm, and an average plate ratio ispreferably 2 to 5.

In the ferromagnetic metal powder, an S_(BET) (specific surface area ofthe BET (Brunauer, Emmett and Teller) method) is usually 40 m²/g to 80m²/g and preferably 50 m²/g to 70 m²/g. A crystal size is usually 10 nmto 25 nm and preferably 11 nm to 22 nm. A pH of the ferromagnetic metalpowder is preferably not less than 7. As the ferromagnetic metalpowders, a single material and alloy of Fe, Ni, Fe-Co, Fe-Ni, Co-Ni,Co-Ni-Fe, and the like are cited, and within a range of not more than 20mass percent of metal compositions can be contained aluminum, silicon,sulfur, scandium, titan, vanadium, chromium, manganese, copper, zinc,yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron,barium, tantalum, tungsten, renium, silver, lead, phosphorus, lanthanum,cerium, praseodymium, neodymium, tellurium, bismuth, and the like. Inaddition, the ferromagnetic metal powders may also contain a smallamount of water, a hydroxide, and an oxide. Manufacturing methods ofthese ferromagnetic metal powders are already well known andferromagnetic metal powders for use in the present invention can also bemanufactured in accordance with well known methods. Although shapes ofthe ferromagnetic metal powders are not particularly restricted, usuallyan acicular shape, a grit shape, a cubic shape, a rice grain shape, aplate shape, and the like are used. It is specifically preferable to useacicular ferromagnetic metal powders.

A coercivity Hc of the ferromagnetic metal powders is preferably 144kA/m to 300 kA/m and more preferably 160 kA/m to 224 kA/m. In addition,a saturation magnetization thereof is preferably 85 A•m²/kg to 150A•m²/kg and more preferably 100 A•m²/kg to 130 A•m²/kg.

As the hexagonal ferrite powders there are a barium ferrite, a strontiumferrite, a lead ferrite, a calcium ferrite, and various replacementmaterials, for example, a Co replacement material, and the like. To bemore precise, are cited a magnetoplumbite type of barium ferrite andstrontium ferrite, the magnetoplumbite type of ferrite whose particlesurface is covered with spinel, further a compound magnetoplumbite typeof barium ferrite and strontium ferrite that partially contain a spinelphase, and the like; and other than predetermined elements, followingones may be contained: Al, Si, S, Ba, Nb, Sn, Ti, V, Cr, Cu, Y, Mo, Rh,Pd, Ag, Sb, Te, W, Re, Au, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, B, Ge,and the like. Generally, the hexagonal ferrite powder where followingcompounds are added can be used: Co-Zn, Co-Ti, Co-Ti-Zr, Co-Ti-Zn,Ni-Ti-Zn, Nb-Zn-Co, Sn-Zn-Co, Sn-Co-Ti, Nb-Zn, and the like. Somehexagonal ferrite powders contain a specific impurity in accordance withmaterials and/or manufacturing methods. The hexagonal ferrite powdersare a hexagonal plate shape.

When reproducing with a magneto resistive head (MR head) to particularlyraise a track density, it is requested to make a noise low: if anaverage plate diameter is too small, a stable magnetization cannot bedesired due to heat fluctuations. In addition, if the average platediameter is too large, the noise is high, thereby both cases being unfitfor the high density recording. Although if the average plate ratio issmall, a filling property in the magnetic layer becomes large and it ispreferable, a sufficient orientation cannot be obtained. If the fillingproperty is too large, the noise becomes high due to stacking betweenpowders. The specific surface area in accordance with the BET method isusually 30 m²/g to 200 m²/g, and 50 m²/g to 100 m²/g is preferable. Thespecific surface area generally accords with an arithmetic calculationvalue from a powder plate diameter and a thickness thereof. Adistribution of the plate diameter and the thickness is preferable to benarrower. Although many distributions are not a normal distribution withbeing calculated in a standard deviation for a powder size, it isexpressed as σ/(average plate diameter or average thickness)=0.1 to 0.5.In order to make a powder size distribution sharp, it is performed tomake a powder generation-reaction system uniform as much as possible andto also dispense a distribution improvement treatment to a generationpowder. For example, such a method of selectively dissolving an ultraminuscule powder in an acid solution is also known. In avitrification-crystallization method a more uniform powder is obtainedby performing heat treatments plural times and separating nucleusgeneration and growth. Although the corercivity Hc measured in amagnetic powder can be made till around 40 kA/m to 400 kA/m, 144 kA/m to300 kA/m is preferable. Although a high Hc is advantageous in the highdensity recording, an ability of a recording head is restricted. An Hccan be controlled by the powder size (plate diameter and platethickness), kinds and amounts of contained elements, replacement sitesof elements, powder generation-reaction conditions, and the like.

A saturation magnetization σs is preferably 30 A•m²/kg to 70 A•m²/kg.The σs tends to become smaller as a powder becomes minuscule. Formanufacturing methods thereof, there are a method of lesseningcrystallization temperature or heat treatment time, another method ofincreasing addition compounds, still another method of increasing anamount of surface treatment, and the like.

In addition, it is possible to use a W type of a hexagonal ferrite. Indispersing the magnetic material a surface of a magnetic powder is alsotreated with a dispersion medium and a material matching a polymer. Aninorganic compound and an organic compound are used as a surfacetreatment agent. As main compounds typical examples are: an oxide andhydroxide of Si, Al, P, and the like; various silane coupling agents;and various titan coupling agents. An amount thereof is 0.1 to 10 masspercent for a magnetic material. A pH thereof is also important fordispersion. It is usually around 4 to 12, and although there is anoptimum value thereof in accordance with the dispersion medium and thepolymer, around 6 to 11 is selected from a chemical stability andstorage stability of the recording medium. A water content contained inthe magnetic material also influences the dispersion. Although there isan optimum value in accordance with the dispersion medium and thepolymer, usually 0.1 to 2.0 mass percent is selected. The presentinvention does not select manufacturing methods although there aremethods as follows: (1) a vitrification-crystallization method of mixingmetal oxides, which replaces a barium carbonate, an iron oxide, and aniron, with such a boron oxide as a glass forming material so as tobecome a predesired ferrite composition, then melting it, making anamorphous material by rapid cooling, next dispensing a reheatingtreatment, and then cleaning and pulverizing it, thereby obtaining abarium ferrite crystalline powder; (2) a water-heat reaction method ofneutralizing a metal salt solution of a barium ferrite composition withalkali, removing byproducts, then heating it in a liquid phase at notless than 100 degrees Celsius, and then cleaning and pulverizing it,thereby obtaining the barium ferrite crystalline powder; and (3) acoprecipitation method of neutralizing the metal salt solution of thebarium ferrite composition with alkali, removing byproducts, then dryingit, performing a heat treatment at not more than 1100 degrees Celsius,and pulverizing it, thereby obtaining the barium ferrite crystallinepowder.

Next, as a second embodiment of the present invention a manufacturingmethod of a magnetic tape will be described. In the second embodiment isdescribed a case of manufacturing the magnetic tape MT1 where amagnetization of all surface of the magnetic tape is oriented in theforward direction.

FIG. 3 is a drawing illustrating a part of a manufacturing process of amagnetic tape.

As shown in FIG. 3, the magnetic tape MT1’ is manufactured by passing abase film BF through a coating process 11, an orientation process 12, adrying process 13, a calendar process 14, and a slitting process 15.Meanwhile, the magnetic tape MT1’ that has finished till the slittingprocess 15 is a tape where a servo signal is not yet recorded.

The base film BF is a wide film comprised of polyethylene terephthalate(PET) and the like.

In the coating process 11 a magnetic paint where magnetic powders aredispersed in a solvent is coated on one face of the base film BF. Inaddition, in some products a back coat layer is also coated.

In the orientation process 12, before the magnetic paint coated in thecoating process 11 is completely dried, an orientation of the magneticmaterial is oriented. A web W where the magnetic paint is coated is madeto pass between two magnets 12a and 12b whose same polarities (Npolarities in the drawing) are made opposite. By sandwiching the web Wwith the same polarities of the magnets like these, magnetic lines thatare parallel to web’s faces and along a longitudinal direction (forwarddirection) can be made, whereby magnetic powders within the magneticpaint before drying are oriented in a same direction as that of amagnetic line (forward direction). Meanwhile, the magnets may be any ofa permanent magnet and an electromagnet.

The drying process 13 dries the magnetic paint by an infrared ray, hotair, and the like.

The calendar process 14 compresses the web W by each roller comprised ofmetal and the like, and heightens a smoothness of a magnetic layersurface.

The slitting process slits the web W whose width is wide into narrowtape forms, and makes them magnetic tapes MT1’, thereby separatelywinding each tape.

FIG. 4 is a configuration drawing of a servo writer used for a processwhere a servo signal is written in a magnetic tape; and FIG. 5 is a planview of a servo write head.

A servo writer 20 is mainly equipped with a supply reel 21, a winder 22,a drive unit 23, a pulse generation circuit 24, a servo write head 25,and a control unit 26. In addition, the servo writer 20 is also equippedwith a power source unit, a cleaning unit for cleaning the magnetic tapeMT1, a verification unit for inspecting written servo signals SS1, andthe like, not shown.

In the supply reel 21 one of the magnetic tapes MT1’ slit into a productwidth from a wide whole web before the servo signals SS1 are written isset in a large diameter winding of a pancake, and the supply reel 21sends out the magnetic tape MT1’ in writing the servo signals SS1. Themagnetic tape MT1’ sent out from the supply reel 21 is carried to theservo write head 25 by being guided with a guide 29 and the like. Andthe magnetic tape MT1 where the servo signals SS1 are written with theservo write head 25 is carried to the winder 22 by being guided withanother guide 29 and the like. The winder 22 is rotated by the driveunit 23, and winds the magnetic tape MT1 where the servo signals SS1 arewritten.

The drive unit 23 is a unit for rotating the winder 22, and is equippedwith a motor not shown, a motor drive circuit for supplying a motorcurrent, a gear for coupling a motor shaft and the winder 22, and thelike. The drive unit 23 generates the motor current in the motor drivecircuit, based on a motor current signal from the control unit 26,supplies the motor current to the motor, and furthermore, transmitsrotation drive force of the motor through the gear, thereby rotating thewinder 22.

The pulse generation circuit 24 is a circuit for supplying the recordingcurrent pulse PC1 (see FIG. 1C), and is equipped with various electroniccomponents. The pulse generation circuit 24 continually generates a pluspulse current PP1 of a plus polarity, a zero current ZC1, another pluspulse current PP1, and another zero current ZC1 in this order, based ona pulse control signal from the control unit 26, and then repeats apattern where no current (zero current ZC) for a predetermined time isgenerated, thereby generating the recording current pulse PC1 (see FIG.1C). And the pulse generation circuit 24 supplies each recording currentpulse PC1 to a coil (not shown) of the servo write head 25. Meanwhile, acurrent value of the plus pulse currents PP1 is an sufficient currentvalue to magnetize a magnetic layer of the magnetic tape MT1’ by a leakmagnetic flux from head gaps 25a, and is set by taking coilcharacteristics of the servo write head 25 into consideration. Inaddition, a pulse width (time) of the plus pulse current PP1 canprescribe a predetermined width of the servo patterns SP1 inlongitudinal directions, and is set by taking a running speed of themagnetic tape MT1’, a shape of the head gaps 25a of the servo write head25, and the like into consideration (see FIG. 5). In addition, apredetermined time of the zero currents ZC1 can prescribe apredetermined interval for forming the servo patterns SP1, and is set bytaking the running speed of the magnetic tape MT1’ and the like intoconsideration.

The servo write head 25 is a head for writing the servo signals SS1, isequipped with the coil (not shown) for generating a magnetic flux, andthe head gaps 25a are formed (see FIG.5). In the head gaps 25a fourpieces of the head gaps 25a are arranged in a line. They are formed by alithography where semiconductor technology is applied, and have abottom-open unparallel reverse V letter shape with a predetermined anglefor longitudinal directions of. the magnetic tape MT1.

The control unit 26 is a unit for controlling operation of each part ofthe servo writer 20, and is equipped with a CPU (Central ProcessingUnit), various memory units, and the like. The control unit 26 generatesthe motor current signal for controlling the motor current of the driveunit 23, and sends it to the drive unit 23. In addition, in order to seta longitudinal direction width of the servo patterns SP1 and the servosignals SS1 that prescribe the predetermined interval for forming theservo patterns SP1, the control unit 26 generates a pulse control signalfor controlling a current value of each plus pulse current PP1, acontrol signal, and a generation timing of the recording current pulsePC1 and sends them to the pulse generation circuit 24. That is, thecontrol unit 26 generates a pulse pattern of a plus pulse current PP1 toa zero current ZC1 to another plus pulse current PP1 to another zerocurrent ZC1.

A process for writing the servo signals SS1 in the magnetic tape MT1’before the signals SS1 are written with using the servo writer thusdescribed will be described.

First, at the supply reel 21 of the servo writer 20 a pancake shape ofthe magnetic tape MT1’ after a slit is set, and a top of the tape MT1’is joined at a core of the winder 22. Here, something to be taken careof in the embodiment of the present invention is to use the magnetictape MT1’ as it is without a demagnetization thereof althoughconventionally the servo signals SS1 are written after a magnetizationgiven in one direction (forward direction) in the orientation process isentirely demagnetized, and then the servo signals SS1 are written.

The magnetic tape MT1’ runs with being wound in the winder 22 that isdriven by the drive unit 23 while the tape MT1’ is guided with theguides 29 and the like. And the servo signals SS1 are written by theservo write head 25 contacting the tape MT1’.

When writing the servo signals SS1, a pulse train of the recordingcurrent pulse PC1 is flowed to the coil of the head gaps 25a of theservo write head 25 at the predetermined pattern. In the recordingcurrent pulse PC1 the currents of a plus pulse current PP1 to a zerocurrent ZC1 to another plus pulse current PP1 to another zero currentZC1 appear at a predetermined period. If the recording current pulse PC1is supplied from the pulse generation circuit 24, the servo write head25 magnetizes the magnetic layer of the magnetic tape MT1’ in thereverse direction by the leak magnetic flux from the head gaps 25a wheneach plus pulse current PP1 flows in the coil; and the head 25 does notmagnetize the magnetic layer of the magnetic tape MT1’ when the currentPC1 is each zero current ZC1. As a result, the servo patterns SP1magnetized in the reverse direction are formed on the servo bands SB1that are the base magnetized in the forward direction of the magnetictape MT1’. Of course, the portion of the servo bands SB1 other than theservo patterns SP1 is magnetized in the forward direction as it is (seeFIG. 1).

The magnetic tape MT1 where the servo signals SS1 are written is woundin the winder 22. Then, it is slit into a tape length in accordance witha product specification, and is put in a cartridge case and the like(not shown).

The magnetic tape MT1 is manufactured by the manufacturing method thusdescribed, and using the tape MT1, the effect described above can beobtained. That is, since a magnetization direction of a base portion ofthe servo bands SB1 and that of the portion of the servo patterns SP1are reverse by 180 degrees, a magnetization change is large at a changeportion between the servo patterns SP1 and the base portion of the servobands SB1, thereby the patterns SP1 being able to be read in a highoutput.

In addition, since the manufacturing method of the second embodimentthus described is a method for writing the servo signals SS1 after theorientation process 12 without a demagnetization, there is an effectthat the method can suppress a manufacturing cost than a conventionalmethod can.

Next, a manufacturing method of a magnetic tape related to a thirdembodiment will be described. In the third embodiment will be describeda case where a magnetic tape MT2 demagnetized on data bands DB2 thereofis manufactured. Meanwhile, in the embodiment a description will beomitted with adding same symbols for same portions in the secondembodiment.

When manufacturing the magnetic tape MT2, first, same as in the secondembodiment, manufacture the magnetic tape MT1’ (see FIG. 3) wheremagnetism is oriented in one direction (forward direction). And writeservo signals SS2 in the magnetic tape MT1’ with a servo writer 20A asshown in FIG. 6A. The servo writer 20A differs from the servo writer 20in the second embodiment (see FIG. 4) in nothing but a point that ademagnetizing head 27a is provided.

The demagnetizing head 27a is an AC delete head provided at an upstreamside of the servo write head 25, with being integrated with the head 25.In the demagnetizing head 27a magnetic gaps (not shown) for ademagnetization are provided at no position except for a lateraldirection position, corresponding to the data bands DB2 formed in themagnetic tape MT2 shown in FIG. 2. Of course, it suffices not todemagnetize a portion of servo bands SB2, and in portions not used forrecording other than the data bands DB2, a demagnetization may beperformed.

In addition, a pulse generation circuit 24a is configured so as tocontinually give demagnetizing signals to the demagnetizing head 27a.

When writing the servo signals SS2 with the servo writer 20A, run themagnetic tape MT1’ sent out of the supply reel 21 while guiding the tapeMT1’ with the guides 29 and the like. And on the way, give thedemagnetizing signals to the demagnetizing head 27a from the pulsegeneration circuit 24a and demagnetize the portion of the data bandsDB2, and then write the servo signals SS2 by magnetizing the magnetictape MT1’ with the servo write head 25 in the reverse direction same asin the second embodiment.

Since in such the servo writer 20A the servo write head 25 and thedemagnetizing head 27a are integrally configured, the writer 20A canleave magnetism in the forward direction of the portion of the servobands SB2 with accurately demagnetizing no portion except for the databands DB2, without receiving an influence of a vibration in running ofthe magnetic tape MT1’.

Meanwhile, although in the embodiment the demagnetizing head 27a isprovided with being integrated with the servo write head 25, thedemagnetizing head 27a may be provided separately from the write head 25like a demagnetizing head 27b of a servo writer B shown in FIG. 6B. Inaddition, the demagnetizing head 27b can also be provided not at anupstream side but at a downstream side.

Furthermore, as another manufacturing method of the magnetic tapes MT1and MT2, a fourth embodiment will be described.

As described above, when generally manufacturing a magnetic tapedifferent from the first and second embodiments, orient particles of amagnetic material by the orientation process 12, fix the particles ofthe magnetic material by the drying process 13, and then defeat amagnetic orientation by a demagnetization process.

When manufacturing the magnetic tape MT1 with using a magnetic tapewhose magnetic orientation is removed, provide a DC delete head 28 atthe upstream side of the servo write head 25 for magnetizing (directcurrent magnetization) the magnetic tape MT1’ over all width thereof.And before writing the servo signals SS1 in a magnetic tape MT1” after ademagnetization of the tape MT1”, magnetize the tape MT1” in advance.Then, if writing the servo signals SS1 with the servo write head 25 sameas in the first embodiment, it can manufacture the magnetic tape MT1where the servo signals SS1 are written in a reverse magnetizationwithin a portion magnetized in the forward direction on all surfacethereof.

In addition, when manufacturing the magnetic tape MT2 with using amagnetic tape whose magnetic orientation is removed, provide magneticgaps corresponding to the servo bands SB2 at no position except for alateral direction position in advance, and magnetize the bands SB2 inthe forward direction with the DC delete head 28 of FIG. 7 describedabove. Then, if writing the servo signals SS2 on the servo bands SB2, itcan manufacture the magnetic tape MT2.

Thus, although the embodiments of the present invention are described,the invention is implemented in various forms without being limited tothe embodiments.

For example, although in the embodiments a recording current is designedto consist of a pulse current where a pulse current of a plus polarityand a zero current are alternately repeated, another pulse current wherea pulse current of a minus polarity and the zero current are alternatelyrepeated may be used.

In addition, although in the embodiments a base portion of servo bandsis magnetized in the forward direction and a portion of servo signals ismagnetized in the reverse direction, on the contrary the base portion ofthe servo bands is magnetized in the reverse direction and then theportion of the servo signals may also be magnetized in the forwarddirection.

1. A magnetic tape where a servo signal for performing tracking controlof a magnetic head is written on a data band and where data is recordedon the data band, wherein said servo signal is written on the servo bandmagnetized in any one of direction of longitudinal directions with beingmagnetized in a reverse direction for said one direction.
 2. A magnetictape according to claim 1, wherein said data band is not magnetized. 3.A magnetic tape according to claim 1, wherein a thickness of a magneticlayer is 10 nm to 300 nm.
 4. A manufacturing method of a magnetic tapeaccording to claim 1, the method comprising: a first process formagnetizing a servo band for writing at least said servo band in any onedirection of longitudinal directions; and a second process for writingsaid servo signal on said servo band in a state where said servo band ismagnetized in one direction by said first process with giving arecording current pulse of a single polarity for magnetizing the servoband in a reverse direction for said one direction to a servo signalrecording head.
 5. A manufacturing method of a magnetic tape accordingto claim 2, the method comprising: a first process for magnetizing aservo band for writing at least said servo signal in any one directionof longitudinal directions; and a second process for writing said servosignal on said servo band in a state where said servo band is magnetizedby said first process with giving a recording current pulse of a singlepolarity for magnetizing the servo band in a reverse direction for saidone direction to a servo signal recording head; and a demagnetizationprocess for demagnetizing said data band at a following process of saidfirst process and at any of a preceding process and a following processof said second process.
 6. A servo writer used for manufacturing amagnetic tape according to claim 1, the writer comprising: a magnetictape travel system for running the magnetic tape sent out from a supplyreel by winding the magnetic tape with a winder; a DC delete head formagnetizing at least said servo band in one direction of longitudinaldirections with contacting said magnetic tape which is running; and aservo write head which is provided at a downstream side of a magnetictape travel direction of said DC delete head, magnetizes said servo bandin a reverse direction with contacting said magnetic tape which isrunning, and writes said servo signal.
 7. A servo writer according toclaim 6, wherein said DC delete head and said servo write head areintegrally configured.
 8. A servo writer used for manufacturing amagnetic tape according to claim 2, the writer comprising: a magnetictape travel system for running said magnetic tape by sending out themagnetic tape, whose all surface is magnetized in one direction oflongitudinal directions, from a supply reel and winding the magnetictape with a winder; a demagnetizing head for demagnetizing said databand with contacting said magnetic tape which is running; and a servowrite head for writing said servo signal, with contacting said magnetictape, which is running, and magnetizing a magnetic layer of said servoband in a reverse direction.
 9. A servo writer according to claim 8,wherein said demagnetizing head and said servo write head are integrallyconfigured.
 10. A magnetic tape according to claim 1, wherein a productof residual magnetism and a thickness of a magnetic layer is 5.0x10⁻¹⁰T•m to 7.5 x10⁻¹⁰ T•m.
 11. A magnetic tape according to claim 1, whereina product of residual magnetism and a thickness of a magnetic layer is5.0x10⁻¹⁰ T•m to 5.0 x10⁻¹⁰ T•m.
 12. A magnetic tape according to claim1, wherein a product of residual magnetism and a thickness of a magneticlayer is 5.0x10⁻¹⁰ T•m to 2.5 x10⁻¹⁰ T•m.
 13. A magnetic tape drive forreading a magnetic tape according to claim 1, wherein a track width of aservo signal reading element is 0.1 μm to 30 μm.
 14. A magnetic tapedrive for reading a magnetic tape according to claim 1, wherein a trackwidth of a servo signal reading element is 0.1 μm to 15 μm.
 15. Amagnetic tape drive for reading a magnetic tape according to claim 1,wherein a track width of a servo signal reading element is 0.1 μm to 7μm.
 16. A magnetic tape according to claim 1, wherein a ferromagneticpowder used for a magnetic layer is any of a ferromagnetic metal powderand a hexagonal ferrite powder.
 17. A magnetic tape according to claim1, wherein an average particle size of a ferromagnetic metal powder is20 nm to 60 nm.
 18. A magnetic tape according to claim 1, wherein aferromagnetic powder is acicular, an average particle size of saidferromagnetic powder is 30 nm to 45 nm, and an average acicular ratio ofsaid ferromagnetic powder is 3 to
 7. 19. A magnetic tape according toclaim 1, wherein a ferromagnetic powder is platy, an average particlesize of said ferromagnetic powder is 25 nm to 35 nm, and an averageplate ratio of said ferromagnetic powder is 2 to
 5. 20. A servo writeraccording to claim 8, wherein a position of said demagnetizing head isat an upstream side of said servo write head for a travel direction ofsaid magnetic tape.
 21. A servo writer according to claim 8, wherein aposition of said demagnetizing head is at a downstream side of saidservo write head for a travel direction of said magnetic tape.